Question: What is the greatest common factor of $40$ and $45$ ? Another way to say this is: $\operatorname{gcf}(40, 45) = {?}$
Answer: The greatest common factor is the largest number that is a factor of both $40$ and $45$ The factors of $40$ are $1$ $2$ $4$ $5$ $8$ $10$ $20$ , and $40$ The factors of $45$ are $1$ $3$ $5$ $9$ $15$ , and $45$ Thus, the greatest common factor of $40$ and $45$ is $5$. $\operatorname{gcf}(40, 45) = 5$